The field of this invention is press felts for use in papermaking machinery, and more particularly press felts for use in the press section of a papermaking machine.
Generally, press felts are used in papermaking machines to support the moist, freshly formed paper web as it encounters a variety of rolls which serve to extract water from the moist paper web. In addition to serving as a support for the paper web, the press felt serves as a receptacle for the water removed from the paper sheet. Thus, it is desirable that the felt contain voids to hold the water removed from the web. The press felt is normally joined into an endless conveyor belt-like shape and during the various operations previously described, a large amount of water builds up in the press felt. The water is removed by suction or various other drainage devices, usually after the paper web and press felt are no longer in direct contact.
In addition to removing water from the web, the press felt also transports the web and drives the press rolls. Because the felt functions as a drive means, there are advantages to forming a portion of the felt from a material that is relatively incompressible. Incompressible materials contribute to the longevity of the fabric's useful life. However, incompressible materials so not normally exhibit those properties required for good removal of the water from the web. For this reason, it has been a common practice to provide a felt with a compressible paper-contacting layer (a batt) which is adhered to an incompressible base fabric. The base fabric does not contact the paper web. It is also possible to provide a compressible roll-contacting layer, adhered to the side of the incompressible base fabric opposite the paper-contacting batt. Thus the woven base layer is sandwiched between the paper-contacting batt or layer and the roll-contacting batt or layer.
Prior art felts suffer from the disadvantage that over time, the constituents of the paper contacting layer are caused by vibration to settle into a more compact configuration, thus reducing the drainage capacity of the felt. Further, the fibers of the prior art papermaking felts tend to loosen from the base layer, come free of the felt and contaminate both the paper web and the working environment.
Accordingly, the present invention achieves the following objects: to provide a papermaker's felt with more efficient drainage and wear resistance characteristics and that better resists compaction and fiber shedding.